Battery diagnostics system and method using second path redundant measurement approach

ABSTRACT

A method for providing battery diagnostics includes: measuring a first voltage across a first battery cell of a rechargeable battery via a first measurement path of a network using a first measurement circuit, measuring the first voltage including taking at least one first voltage sample during a first time period using the first measurement circuit; measuring a second voltage across the first battery cell via a second measurement path of the network using a second measurement circuit, measuring the second voltage including taking at least one second voltage sample during the first time period using the second measurement circuit, where the second measurement path of the network is different from the first measurement path of the network; comparing the measured first voltage with the measured second voltage; and generating a diagnostic output signal based on the comparison.

This application is a continuation of U.S. patent application Ser. No.15/923,635, filed on Mar. 16, 2018, which application is herebyincorporated herein by reference.

TECHNICAL FIELD

The present invention relates generally to an electronic system andmethod, and, in particular embodiments, to a battery diagnostics systemand method using second path redundant measurement approach.

BACKGROUND

Electric vehicles are vehicles that use an electric motor forpropulsion. Typically, an electric vehicle uses a battery pack to powerthe electric motor. A battery pack typically includes a stack of batterycells in series to achieve voltages such as 400 V, or higher. Forexample, a battery pack may include a stack of 96 lithium-ion batterycells connected in series. Voltages lower than 400 V may also be used.

Since electric vehicles are typically powered by a battery pack, thehealth of the battery pack is a major safety concern. In some cases,failure of a single battery cell of the battery pack may becatastrophic. For example, due to manufacturing or usage-relatedvariations, some battery cells may have slightly less capacity thanother battery cells in the battery pack. Without battery cell balancing,one or more battery cells may fail after multiple charge/dischargecycles.

Vehicles, therefore, typically monitor and periodically rebalance eachindividual battery cell. The monitoring and balancing of the batterycells is typically done by an external integrated circuit (IC), oftencalled battery stack monitor, battery monitor IC or sensing IC, which isconnected to the battery pack via a balancing network. In someimplementations, the external IC monitors the voltage across eachbattery cell of the battery pack and then discharges some of the batterycells based on the monitored voltage to ensure that each battery cell isbalanced with respect to the other battery cells in the battery pack.Since the balancing network used to connect the external IC to thebattery pack may fail, the external IC may be capable to detect opencircuits of the balancing network as another diagnostic feature.

SUMMARY

In accordance with an embodiment, a method for providing batterydiagnostics includes: measuring a first voltage across a first batterycell of a rechargeable battery via a first measurement path of a networkusing a first measurement circuit, measuring the first voltage includingtaking at least one first voltage sample during a first time periodusing the first measurement circuit; measuring a second voltage acrossthe first battery cell via a second measurement path of the networkusing a second measurement circuit, measuring the second voltageincluding taking at least one second voltage sample during the firsttime period using the second measurement circuit, where the secondmeasurement path of the network is different from the first measurementpath of the network; comparing the measured first voltage with themeasured second voltage; and generating a diagnostic output signal basedon the comparison.

In an embodiment, a circuit includes: a first measurement circuitconfigured to be coupled to a first battery cell via a first path of anetwork; a second measurement circuit configured to be coupled to thefirst battery cell via a second path of the network, the second pathbeing different than the first path; and a controller configured to:cause the first measurement circuit to measure a first plurality ofvoltage samples across first and second terminals of the first batterycell during a first time period, cause the second measurement circuit tomeasure a second plurality of voltage samples across the first andsecond terminals of the first battery cell during the first time period,compare an output of the first measurement circuit with an output of thesecond measurement circuit, and generate a diagnostic output signalbased on the comparison.

In an embodiment, a battery management system includes: a rechargeablebattery including N battery cells coupled in series, where N is apositive integer greater than zero; a balancing network coupled to therechargeable battery; and a battery monitoring circuit coupled to thebalancing network, the battery monitoring circuit including: asigma-delta analog-to-digital converter (ADC) having an input configuredto be coupled to a first battery cell of the N battery cells via a firstpath of the balancing network, the sigma-delta ADC coupled to a firstreference voltage generator; a measurement circuit having an inputconfigured to be coupled to the first battery cell via a second path ofthe balancing network, the second path being different from the firstpath, the measurement circuit coupled to a second reference voltagegenerator different from the first reference voltage generator, themeasurement circuit having a different architecture than the sigma-deltaADC; and a controller configured to: control the sigma-delta ADC tomeasure a first plurality of voltage samples across first and secondterminals of the first battery cell during a first time period, controlthe measurement circuit to measure a second plurality of voltage samplesacross the first and second terminals of the first battery cell duringthe first time period, compare an output of the sigma-delta ADC with anoutput of the measurement circuit, and generate a diagnostic outputsignal based on the comparison.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, and theadvantages thereof, reference is now made to the following descriptionstaken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of a portion of a battery managementsystem, according to an embodiment of the present invention;

FIG. 2 shows a flow chart of an embodiment method of detecting a failureof a battery management system, according to an embodiment of thepresent invention;

FIG. 3 shows a schematic diagram of a portion of a battery managementsystem, according to another embodiment of the present invention;

FIG. 4 shows a schematic diagram of a portion of a battery managementsystem, according to an embodiment of the present invention;

FIG. 5 shows a schematic diagram of a portion of a battery managementsystem, according to another embodiment of the present invention;

FIG. 6 shows a schematic diagram of a portion of a battery managementsystem, according to yet another embodiment of the present invention;

FIG. 7 shows a schematic diagram of a portion of a battery managementsystem, according to an embodiment of the present invention;

FIG. 8 shows a schematic diagram that illustrates a possible measurementsystem for achieving simultaneous measurements, according to anembodiment of the present invention;

FIG. 9 illustrates timing diagrams for measuring voltage across each ofthe battery cells of the battery management system of FIG. 7 , accordingto an embodiment of the present invention;

FIG. 10 shows a schematic diagram of a portion of a battery managementsystem, according to another embodiment of the present invention; and

FIG. 11 shows a flow chart of an embodiment method of detecting afailure of a battery management system, according to an embodiment ofthe present invention.

Corresponding numerals and symbols in different figures generally referto corresponding parts unless otherwise indicated. The figures are drawnto clearly illustrate the relevant aspects of the preferred embodimentsand are not necessarily drawn to scale. To more clearly illustratecertain embodiments, a letter indicating variations of the samestructure, material, or process step may follow a figure number.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The description below illustrates the various specific details toprovide an in-depth understanding of several example embodimentsaccording to the description. The embodiments may be obtained withoutone or more of the specific details, or with other methods, components,materials and the like. In other cases, known structures, materials oroperations are not shown or described in detail so as not to obscure thedifferent aspects of the embodiments. References to “an embodiment” inthis description indicate that a particular configuration, structure orfeature described in relation to the embodiment is included in at leastone embodiment. Consequently, phrases such as “in one embodiment” thatmay appear at different points of the present description do notnecessarily refer exactly to the same embodiment. Furthermore, specificformations, structures or features may be combined in any appropriatemanner in one or more embodiments.

The present invention will be described with respect to embodiments in aspecific context, a diagnostic circuit coupled to a battery pack of anelectric vehicle and configured to detect faults in the battery pack,balancing network, and other components internal and external to thediagnostic circuit by using a redundant voltage measurement circuitsimplemented with different technologies. Some embodiments may be used insystems other than an electric vehicle, such as other systems thatmeasure voltage. Technologies to measure voltage other than the onesdescribed herein may also be used.

System redundancy may be used in safety critical systems, such asbattery management systems, to decrease the failure probability of thesystem. The decrease in the probability of failure is generally mosteffective when the redundant system and the primary system areuncorrelated (i.e., mutually exclusive). For example, typically, theless the correlated the redundant measurement system is with the primarysystem, the lower the probability that the primary system and theredundant system fail as a result of a single specific event or rootcause (also known as common cause failure).

In an embodiment of the present invention, a battery management systemuses a battery monitor IC that uses redundancy to monitor the voltageacross each battery cell of a battery pack. The voltage across a batterycell is measured with a primary voltage measurement circuit and with asecondary voltage measurement circuit. The primary and secondary voltagemeasurement circuits are implemented with different technologies, usedifferent reference voltage generators, and measure the voltage acrossthe battery cell simultaneously via different paths. Faults internal tothe battery monitor IC or external to the battery monitor IC, such asfaulty components and leaky paths, may be detected by comparing adifference between the voltages measured by the primary and secondaryvoltage measurement circuits with a voltage threshold.

FIG. 1 shows a schematic diagram of battery management system 100,according to an embodiment of the present invention. Some components anddetails of battery management system 100 have been omitted for claritypurposes. Battery management system 100 includes battery pack 101coupled to battery monitor IC 102 via analog filter and balancingnetwork 104. Battery monitor IC 102 includes electrostatic discharge(ESD) protection circuit 106, open-loop diagnostics and balancingcircuit 108, and voltage measurement circuit 109. Battery pack 101includes a plurality of battery cells coupled in series. However, FIG. 1illustrates only battery cell cell_(i) of battery pack 101 for claritypurposes.

During normal operation, the voltage across battery cell cell_(i) ismonitored by voltage measurement circuit 109. The voltage measured byvoltage measurement circuit 109 is used, for example, to determinewhether battery cell cell_(i) should be discharged to be balanced withrespect to other battery cells in battery pack 101. The voltage acrossbattery cell cell_(i) may also be used to determine whether battery cellcell_(i) is discharged, or over-charged. The voltage across battery cellcell_(i) may also be used for other purposes, such as to recalibrate asystem-on-chip (SoC) in open circuit voltage (OCV).

Voltage measurement circuit 109 includes redundancy for measuring thevoltage across battery cell cell_(i). For example, voltage measurementcircuit 109 includes voltage measurement circuit 110 and voltagemeasurement circuit 112. Voltage measurement circuits 110 and 112 may beimplemented with different measurement schemes. Different measurementschemes involve a different architecture (e.g., SAR ADC or Σ-Δ ADC)and/or a different measurement principle. For instance, voltagemeasurement circuit 110 could be implemented as a 13-bit Σ-Δ ADC with aspecific digital filtering and voltage measurement circuit 112 could beimplemented as a 16-bit Σ-Δ ADC using a different digital filtering.Each of the voltage measurement circuits 110 and 112 uses a differentreference voltage. Reference generator 111 and 113 generate thereference voltages for voltage measurement circuits 110 and 112,respectively.

As shown in FIG. 1 , voltage measurement circuit 110 measures thevoltage across battery cell cell_(i) using path 122 and voltagemeasurement circuit 112 measures the voltage across battery cellcell_(i) using path 124. Paths 112 and 124 use different pins of batterymonitor IC 102 and use different components of analog filter andbalancing network 104. Paths 112 and 124 may also be exposed todifferent ESD structures, since each pin of battery monitor IC 102 hasits own ESD protection circuit. The ESD structures of the pins of IC 102are collectively shown in FIG. 1 as ESD protection circuit 106 forclarity purposes. Paths 112 and 124 may also be exposed to differentcircuits of open-loop diagnostics and balancing circuit 108 (dependingon the implementation of open-loop diagnostics and balancing circuit108).

Both voltage measurement circuits 110 and 112 measure the voltage acrossbattery cell cell_(i) at the same time. The filtering characteristics ofpaths 112 and 124 are dimensioned to allow for a comparable result whenmeasuring the same signal at the same time by both measurement circuits110 and 112.

Reference generator circuits 111 and 113 may be implemented in any wayknown in the art. For example, reference generator circuits 111 and 113may be implemented by using independent band-gap circuits that supplyindependent voltages to be used as references for the voltagemeasurement units 112 and 110. In some embodiments, the architecture ofthe respective band-gap circuits and voltage regulators may bedifferent. In other embodiments, the architecture of reference generatorcircuits 111 and 113 may be identical. Other implementations are alsopossible.

Open-loop diagnostics and balancing circuit 108 detects whether an opencircuit condition exists in analog filter and balancing network 104 byperforming an open-loop test. Open-loop diagnostics and balancingcircuit 108 also discharges battery cell cell_(i) to a desired voltageto balance battery cell cell_(i) with respect to other battery cells inbattery pack 101. Open-loop diagnostics and balancing circuit 108 may beimplemented in any way known in the art. For example, typicalimplementations include current sources, comparators, and transistors.

Analog filter and balancing network 104 includes a balancing networkthat includes resistors and an analog filter that includes capacitorsthat provide filtering in combination with the resistors of thebalancing network. As a non-limiting example, in some embodiments,resistors R₁ have a resistance of 5Ω, resistor R₂ has a resistance of20Ω, and capacitors C₁ have a capacitance of 330 nF. Other resistanceand capacitance values may be used. For example, the resistances ofresistors R₁ and R₂ and the capacitances of capacitors C₁ may beselected based on the filtering characteristics desired to allow for themeasurements and of 112 and 110 to be comparable when measuring the samesignal at the same time. In some embodiments, the filteringcharacteristics of balancing network may be supplemented by subsequentfiltering after sampling the voltage to obtain a matching totaleffective filtering characteristic. Analog filter and balancing network104 may be implemented with other arrangements, such as shown, forexample, in FIGS. 3 and 4 .

ESD protection circuit 106 provides a path for ESD discharge to some orall pins of battery monitor IC 102. ESD protection circuit 106 may beimplemented in any way known in the art. For example, ESD diodes may becoupled in a reverse biasing configuration between a pin (e.g., U_(i))and a ground node and/or a battery supply node and/or another pin ofbattery monitor IC 102. Other implementations are also possible.

Battery monitor IC 102 is implemented in a monolithic semiconductorsubstrate. In some embodiments, battery monitor IC 102 may beimplemented in a multi-chip architecture, where, for example, voltagemeasurement circuit 110 is disposed in a first monolithic semiconductorsubstrate together with reference generator in, and voltage measurementcircuit 112 is disposed together with reference generator 113 in asecond monolithic semiconductor substrate different than the firstmonolithic semiconductor substrate and packaged in the same package.Other implementations are also possible.

Battery pack 101 includes a plurality of battery cells. For example,battery pack 101 may include 12 rechargeable lithium ion battery cellsstacked in series. A different number of battery cells stacked in seriesmay also be used. In some embodiments, stacks of battery cells coupledin series may be coupled to other stacks of battery cells in paralleland/or in series. For example, a battery pack may include 4 stacks of 8series connected battery cell stacks, where the 4 stacks are connectedin parallel, and where each of the 8 series connected battery cellstacks includes 12 lithium ion battery cells connected in series. Somebattery packs may use battery cells with a different chemistry. Forexample, some battery packs may use other lithium based chemistries.Other chemistries may be used.

Advantages of some embodiments include the increase of the common causerobustness of the battery management system by having redundant voltagemeasurement circuits that rely on independent measurement circuitsimplemented with different measurement technologies, and using differentreference voltages and different measurement paths. Some embodimentsfurther improve the diagnostics capabilities by performing statisticalanalysis between the voltage measurements of both voltage measurementcircuits, such as, for example, checking for correlation between themeasurements measured by both voltage measurement circuits.

FIG. 2 shows a flow chart of embodiment method 200 of detecting afailure of a battery management system, according to an embodiment ofthe present invention. Method 200 may be implemented using batterymanagement system 100. Alternatively, method 200 may be implemented inother battery management system implementations. The discussion thatfollows assumes that battery management system 100, as shown in FIG. 1 ,implements method 200.

During step 202, a voltage across a battery cell, such as battery cellcell_(i) of battery pack 101, is measured by a first voltage measurementcircuit, such as, for example, voltage measurement circuit 110. Thefirst voltage measurement circuit is coupled to the battery cell via anetwork, such as analog filter and balancing network 104. The firstvoltage measurement circuit measures the voltage across the battery cellvia a first path during a first time.

During step 204, the voltage across the battery cell is measured by asecond voltage measurement circuit, such as, for example, voltagemeasurement circuit 112, which is different than the first voltagemeasurement circuit. The second voltage measurement circuit measures thevoltage across the battery cell via a second path during the first time.In other words, the first voltage measurement circuit and the secondvoltage measurement circuit simultaneously measure the voltage acrossthe battery cell via different paths.

During step 206, the voltage measured by the first voltage measurementcircuit is compared with the voltage measured by the second voltagemeasurement circuit. If the voltages measured by the first and secondvoltage measurement circuits are substantially equal (e.g., thedifference between the measurements is lower than or equal to a voltagethreshold V_(th)), the battery management system is operating normally,and the measured voltage may be used for other purposes, such as, forexample, deciding whether to rebalance the battery cell or stopcharging. If the voltages measured by the first and second voltagemeasurement circuits are different (e.g., the difference between themeasurements is higher than the voltage threshold V_(th)), a fault isdetected.

Since the first and second voltage measurement circuits are measuringthe same signal at the same time with comparable filters, sudden changesin the voltage of the battery cell will be equally captured by bothvoltage measurement circuits. Such common mode rejection allows for thesetting of a low voltage threshold V_(th) for determining whether afault exists. Using a low voltage threshold V_(th) may allow for thedetection of faults such as leakage of the capacitor of analog filterand balancing network 104, leakage in pins U_(i) and/or G_(i) of thebattery monitor IC 102, leakage in the ESD structures, and leakage intransistors 116 and/or 118

In some embodiments, for example using lithium-ion battery cells, it isdetermined that the first and second voltages are substantially equal ifthe absolute value of the difference between the first and secondvoltages is lower than a voltage threshold V_(th) of, e.g., 10 mV. Lowerthreshold values, e.g., 5 mV or lower, or higher threshold values, e.g.,20 mV, 50 mV or higher, may also be used.

Advantages of some embodiment include the detection of faults beyondopen loop detection. For example, leakage in various components internalto the battery monitor IC and external to the battery monitor IC may bedetected.

FIG. 3 shows a schematic diagram of a portion of battery managementsystem 300, according to another embodiment of the present invention.Battery management system 300 operates in a similar manner than batterymanagement system 100 and may implement method 200 of detecting afailure of the battery management system. However, battery managementsystem 300 includes two different pins along the different paths formonitoring each node across battery cell cell_(i). For example, nodeBC_(i) may be accessed using path 310 via pin U_(i) or via path 312using pin G_(i-1), and node BC_(i-1) may be accessed using path 310 viapin or via path 312 using pin G_(i-2).

In some embodiments, voltage measurement circuit 110 is used as aprimary measurement circuit to accurately measure the voltage acrossbattery cell cell_(i) using pins U_(i) and while voltage measurementcircuit 112 is used as a secondary measurement circuit for safetyreasons to verify the voltage measured by measurement circuit 110 usingpins G_(i-1) and G_(i-2). By using two independent pins for thesecondary measurement circuit as shown in FIG. 3 , the voltage measuredby the secondary measurement circuit is not influenced, e.g., bybalancing currents. For example, balancing currents may flow into pinG_(i-1) and out through pin G_(i-2).

Advantages of some embodiments include the inclusion of a redundantvoltage measurement path by reusing existing structures of the balancingnetwork, as shown, for example, in FIGS. 1 and 3 .

FIG. 4 shows a schematic diagram of a portion of battery managementsystem 400, according to an embodiment of the present invention. Somecomponents and details of battery management system 400, such as ESDstructures and open-loop diagnostics and balancing circuits, have beenomitted for clarity purposes. Battery management system 400 includes nbattery cells arranged in series coupled to battery monitor IC 402 viaanalog filter and balancing network 404. Battery monitor IC 402 includesn voltage measurement circuits 410 and n voltage measurement circuits412. Each battery cell is coupled to a respective voltage measurementcircuit 410 and voltage measurement circuit 412 via analog filter andbalancing network 404.

In some embodiments, n may be 12. In such embodiments, voltage at pin VSmay be, for example, about 60 V during normal operation. Otherembodiments may be implemented with n smaller than 12, such as forexample, 6 or lower. Other embodiments may be implemented with valueshigher than 12, such as 15, 24, or higher.

As shown in FIG. 4 , each of the redundant measurement voltage circuitsis coupled to the respective battery cell via 3 pins, similar to theconfiguration shown in FIG. 1 . Some embodiments may implement batterymanagement system 400 using a 4 pin configuration, such as shown in FIG.3 .

By having n voltage measurement circuits 410 and n voltage measurementcircuits 412, battery management system 400 can simultaneously measurethe voltage across each of the n battery cells. In other words, all thebattery cells of battery pack 101 may have their associated voltagesmeasured simultaneously and redundantly by the respective voltagemeasurement circuits 410 and 412.

Some embodiments may use one or more multiplexers (MUXs) to share avoltage measurement circuit between two or more battery cells. Forexample, FIG. 5 shows a schematic diagram of a portion of batterymanagement system 500, according to an embodiment of the presentinvention. Battery management system 500 operates in a similar mannerthan battery management system 400. Battery management system 500,however, shares voltage measurement circuit 510 over the n battery cellsof battery pack 101 using MUX 505 instead of having n voltagemeasurement circuits 510.

Battery management system 500 simultaneously measures the voltage acrosseach of the n battery cells of battery pack 101 using voltagemeasurement circuit 510 and the respective voltage measurement circuit512. For example, the voltage across battery cell cell₁ is measuredsimultaneously by measurement circuit 512 ₀ and by voltage measurementcircuit 510, where MUX 505 is configured to select the channelsassociated with battery cell cell₁. After the voltage across batterycell cell₁ is measured, the voltage across battery cell cell₂ may bemeasured simultaneously by measurement circuit 512, and by voltagemeasurement circuit 510, where MUX 505 is configured to select thechannels associated with battery cell cell₂. The sequence is repeatedfor each of the battery cells in battery pack 101, although notnecessarily in that order.

As shown in FIG. 5 , voltage measurement circuit 510 is shared over then battery cells of battery pack 101. Some embodiments, may share avoltage measurement circuit 510 over k battery cells, where k is smallerthan or equal to n.

Some embodiments may also share voltage measurement circuit 512 overmore than one battery cells. For example, FIG. 6 shows a schematicdiagram of a portion of battery management system 600, according to anembodiment of the present invention. Battery management system 600operates in a similar manner than battery management system 500. Batterymanagement system 600, however, shares voltage measurement circuit 512over the n battery cells of battery pack 101 using MUX 604 instead ofhaving n voltage measurement circuits 512.

Battery management system 600 simultaneously measures the voltage acrosseach of the n battery cells of battery pack 101 using voltagemeasurement circuits 510 and 612. For example, the voltage acrossbattery cell cell₁ is measured simultaneously by measurement circuit 510and 612, where MUXes 505 and 604 are respectively configured to selectthe channels associated with battery cell cell₁. After the voltageacross battery cell cell₁ is measured, the voltage across battery cellcell₂ may be measured simultaneously by measurement circuits 510 and612, where MUXes 505 and 604 are respectively configured to select thechannels associated with battery cell cell₂. The sequence is repeatedfor each of the battery cells in battery pack 101, although notnecessarily in that order.

As shown in FIG. 6 , voltage measurement circuit 612 is shared over then battery cells of battery pack 101. Some embodiments, may share avoltage measurement circuit 612 over j battery cells, where j is smallerthan n. In some embodiments, j may be equal to k. In some embodiments,j, k and n may be equal to each other.

FIG. 7 shows a schematic diagram of a portion of battery managementsystem 700, according to an embodiment of the present invention. Batterymanagement system 700 includes battery pack 701 (which has for example12 lithium ion battery cells), and battery monitor IC 702 coupled tobattery pack 701 via analog filter and balancing network 703. Batterymanagement system 700 operates in a similar manner than batterymanagement system 600. Battery management system 700, however,implements voltage measurement circuit 612 with SAR ADC 706 andimplements 12 Σ-Δ ADC 704, each coupled to the respective battery cellof battery pack 701 via analog filter and balancing network 703 insteadof a single voltage measurement circuit 510 coupled to the battery packvia MUX 505. Reference generator 111 provides reference voltage V_(ref1)to all 12 Σ-Δ ADC 704 while reference generator 113 provides referencevoltage V_(ref2) to SAR ADC 706.

During normal operation, controller 702 configures MUX 604 to select achannel (e.g., CH₀) associated with a particular battery cell (e.g.,cell₁) and configures SAR ADC 707 and the respective Σ-Δ ADC 704 (e.g.,Σ-Δ ADC 704 ₀) to measure the voltage across the particular battery cellsimultaneously. The process is repeated for each of the battery cells inbattery pack 701.

As known, although Σ-Δ ADC 704 and SAR ADC 706 each produce a digitalvalue associated with the sampled analog voltage at the input, Σ-Δ ADC704 and SAR ADC 706 produces their respective digital value by using adifferent architecture and operating principle. For example, a SAR ADCtypically samples and holds an analog voltage sample at the ADC input,and then generates a voltage with an m-bit DAC and compares the voltagegenerated from the m-bit DAC with the voltage sampled at the input usinga comparator. The digital output produced by the SAR ADC is the digitalcode that when used to configure the m-bit DAC generates the voltagethat is closest to that of the sampled input. Typically, a SAR ADC usesbinary search to find such m-bit DAC code. The m-bit DAC typically has8, 10, 12, or more bits.

A Σ-Δ ADC uses a combination of oversampling and noise shapingtechniques to convert the analog input into a digital output. Typically,a 1-bit DAC is used in combination with a differentiator, an integratorand digital filtering to produce the digital code. In contrast to theSAR ADC, the Σ-Δ ADC is mostly implemented using digital logic ratherthan analog components. SAR ADCs and Σ-Δ ADCs are well known in the artand will not be discussed further.

Since Σ-Δ ADCs and SAR ADCs typically have different sampling rates, thefiltering characteristics of analog filter and balancing network 703 maybe designed to prevent aliasing for both types of ADCs. In someembodiments, anti-aliasing is achieved by reducing noise to values lowerthan e.g., 1 mV, at a frequency fs/2, where fs is the sampling frequencyof the slowest ADC (e.g., SAR ADC).

Battery monitor IC 702 is implemented in a monolithic semiconductorsubstrate. In some embodiments, battery monitor IC 702 may beimplemented in a multi-chip architecture, where, for example, SAR ADC706 and MUX 604 are disposed in a first monolithic semiconductorsubstrate together with reference generator in, and Σ-Δ ADC 704 aredisposed together with reference generator 113 in a second monolithicsemiconductor substrate different than the first monolithicsemiconductor substrate and packaged in the same package. Otherimplementations are also possible.

FIG. 8 shows a schematic diagram of measurement system 800 for achievingsimultaneous measurements, according to an embodiment of the presentinvention. Measurement system 800 simultaneously measures the voltageacross cell cell_(i) for the same duration of time with primarymeasurement circuit 804 and secondary measurement circuit 810 andgenerates a primary measurement result and a secondary measurementresult based on the respective measured voltage. In some embodiments,voltage measurement circuit 110 may be implemented as primarymeasurement circuit 804 and voltage measurement circuit 112 may beimplemented as secondary measurement circuit 810.

Measurement system 800 includes primary measurement circuit 804,secondary measurement circuit 810, and anti-aliasing filters 802 and808. In some embodiments, antialiasing filters 802 and 808 correspond toanalog filters and balancing networks (e.g., such as 104, 404 and 703,previously described). FIG. 8 shows a primary measurement result and asecondary measurement result each having 16 bits. It is understood thatother values, such as 8 bits, 12 bits, 14 bits, 24 bits, 32 bits, may beused.

Primary measurement circuit 804 has a total effective filteringcharacteristic that includes the filtering characteristics ofanti-aliasing filter 802 and sampling and averaging block 806. Secondarymeasurement circuit 810 has a total effective filtering characteristicthat includes the filtering characteristics of anti-aliasing filter 808,and sampling block 812 and digital averaging block 814. The totaleffective filtering characteristics of primary measurement circuit 804and secondary measurement circuit 810 are dimensioned to allow formeasuring the same signal at the same time by both measurement circuits804 and 810.

In some embodiments, the total effective filtering characteristics ofmeasurement circuits 804 and 810 is matched by having similar dominantpoles and similar step responses. As a non-limiting example, in anembodiment where primary measurement circuit 804 is implemented with aΣ-Δ ADC, and secondary measurement circuit 810 is implemented with a SARADC, anti-aliasing filter 802 may have a pole of about 500 kHz, the Σ-ΔADC has a sampling and averaging block 806 that may sample therespective input signal at about 20 MHz and have an averaging N-orderfilter with a pole at about 100 Hz, where n may be greater or equal to1, anti-aliasing filter 808 may have a pole of about 10 kHz, the SAR ADChas a sampling block 812 that may sample the input signal at about 400Hz, and an N-order digital averaging block 814 may perform digitalaveraging with a pole at about 100 Hz. In this example, the dominantpole of each of measurements circuits 804 and 810 is about 100 Hz withthe same frequency slope (e.g., 20 dB per decade when n is equal to 1).Other values for the pole frequencies, sampling frequencies and order ofthe filters may be used.

Some embodiments may achieve similar (matched) total effective filteringcharacteristics without having equal dominant poles that decay at thesame rate. For example, in some embodiments, primary measurement circuit804 may have a first order pole at 100 Hz and a first order pole at 105Hz while secondary measurement circuit 810 may have a second order poleat 99 Hz. In such embodiment, the total effective filteringcharacteristic of primary measurement circuit 804 is considered asmatching the total effective filtering characteristic of secondarymeasurement circuit 81 o. Other filtering characteristics and othervalues for the dominant poles and frequency slopes may be used.

In some embodiments, the Σ-Δ ADC is implemented with a first ordercascaded integrator-comb (CIC) filter. The CIC filter may be implementedin any way known in the art.

In some embodiments, measurements circuits 804 and 810 may beimplemented in the same manner. For example, in some embodiments,measurement circuits 804 and 810 may both be implemented with Σ-Δ ADCs.In some embodiments, measurement circuits 804 and 810 may both beimplemented with SAR ADCs. In yet other embodiments, primary measurementcircuit 804 is implemented with a Σ-Δ ADC while secondary measurementcircuit 810 is implemented with comparators. Other implementations arealso possible.

FIG. 9 illustrates timing diagrams for measuring voltage across each ofthe 12 battery cells of battery pack 701, according to an embodiment ofthe present invention. Waveform 904 corresponds to conversion timing ofΣ-Δ ADC 704. Waveform 906 corresponds to conversion timing of SAR ADC706 and associated MUX 604. Waveform 905 is a zoomed-in version of aportion of waveforms 904 and 906.

As shown in FIG. 9 , during diagnostic time t_(CH_Diagnose) the voltageacross each of the 12 battery cells of battery pack 701 are measured.For example, during time t_(cho), Σ-Δ ADC 704 ₀ measures the voltageacross battery cell cell₁ while SAR ADC 706 measures the voltage acrosschannel CH₀ of MUX 604, which is associated with the voltage acrossbattery cell cell₁. During time t_(ch1), Σ-Δ ADC 7041 measures thevoltage across battery cell cell₂ while SAR ADC 706 measures the voltageacross channel CH₁ of MUX 604, which is associated with the voltageacross battery cell cell₂. The sequence is repeated for all the 12battery cells of battery pack 701.

As shown in waveform 905, SAR ADC 706 and the respective Σ-Δ ADC 704measures the voltage across the respective battery cell at the same timeand for the same duration of time. In other words, even though SAR ADC706 typically collects a smaller number of samples than Σ-Δ ADC 704during the measurement time, the time during which the samples arecollected should be the same. The samples collected by each ADC duringthe measurement time are then respectively averaged (e.g., by using alow pass filter) to obtain a respective final value. For example, thefrequency J of Σ-Δ ADC 704 and the number of Q input samples taken byΣ-Δ ADC 704 are selected to take the same time as the time taken by SARADC 706 to take L samples at a frequency P. As a non-limiting example,if the duration of time t_(cho) is 75 μs, SAR ADC 706, which operates at666 kHz, collects 50 input samples while Σ-Δ ADC 704 ₀ takes 1024samples of the input signal while operating at an over-sampling rate of13.65 MHz. In some embodiments, time t₁ between conversions isminimized, for example, to 1 μs.

FIG. 10 shows a schematic diagram of a portion of battery managementsystem 1000, according to an embodiment of the present invention.Battery management system 1000 includes battery pack 701 and batterymonitor IC 1002 coupled to battery pack 701 via analog filter andbalancing network 703. Battery management system 1000 operates in asimilar manner than battery management system 400. Battery managementsystem 1000, however, implements each voltage measurement circuit 410with a respective Σ-Δ ADC 704 and each of the voltage measurementcircuits 512 with a respective comparator circuit 1008. Referencegenerator 111 provides reference voltage V_(ref1) to all 12 Σ-Δ ADC 704while reference generator 113 provides reference voltage V_(ref2) to DAC1016, which provides a reference to all comparator circuits 1008.

During normal operation, each of the comparator circuits 1008 operatesas a window comparator. The high threshold and low threshold of eachcomparator circuit 1008 is provided by DAC 1016.

During the measurement time, the respective Σ-Δ ADC 704 collects samplesand generates a digital value associated with the measured voltage whilethe respective comparator circuit 1008 generates a plurality ofcomparison results and generates as a final value the most frequentcomparison result. For example, assuming that battery cell₁ has voltageV₃ (e.g., 3.6 V) across its terminals, Σ-Δ ADC 704 ₀ collects aplurality of samples during a first measurement time and generates as aresult a digital value that corresponds to 3.6 V. During the same firstmeasurement time, comparator circuit 1008 ₀ compares the value at itsinputs with the values provided by DAC 1016 and, for each comparison,generates a value (e.g., 0) representative of the input being outsidethe window if the voltage is outside the window and a value (e.g., 1)representative of the input being inside the window if the voltage isinside the window. If comparator circuit 1008 ₀ generates Z samples(e.g., 100 samples), of which more samples (e.g., 51 or more) are insidethe window (e.g., 1) and less samples (e.g., 49 or less samples) areoutside the window (e.g., 0), the final result is that the input isinside the window (e.g., 1), which means that the sampled voltage iswithin the limits provided by DAC 1016. If instead, out of the Zsamples, more samples are outside the window (e.g., 0) and less samplesare inside the window (e.g., 1), the final result is that the input isoutside the window (e.g., 0), which means that the sampled voltage isoutside the window provided by DAC 1016. The same measurement isperformed for each battery cell of battery pack 701. In this way,comparator circuits 1008 may be used to verify that the voltage measuredby the respective Σ-Δ ADC 704 is inside the window specified by DAC1016.

In some embodiments, comparator circuit 1008 ₀ generates a 0 when theinput is outside the window and a 1 when the input is inside the window.In other embodiments, comparator circuit 1008 ₀ generates a 1 when theinput is outside the window and a 0 when the input is inside the window.In other embodiments, comparator circuit 1008 ₀ generates a negativevalue when the input is outside the window and a positive value when theinput is inside the window. In other embodiments, comparator circuit1008 ₀ generates a positive value when the input is outside the windowand a negative value when the input is inside the window. Otherimplementations are possible.

In some embodiments, DAC 1016 may set the high threshold to the samelevel as the maximum recommended operating voltage for the battery cell(e.g., 4.5 V for a lithium ion cell) and the low threshold to theminimum operating voltage for the battery cell (e.g., 2.7 V for alithium ion cell). Other embodiments may implement a tighter window,such as, for example, a 50 mV window, or lower.

The voltage curve of a battery cell, such as a lithium battery cell,across different charge levels is not linear. For example, when alithium battery cell is fully charged, the voltage across the batterycell may be as high as 4.2 V or higher, and when the lithium batterycell is discharged, the voltage across the battery cell may be 3 V orlower. During most of the time (e.g., from 80% charge level to 20%charge level) the voltage may be about 3.6 V. To achieve a tight window(of e.g., 5 mV) of comparison for comparator circuits 1008 duringdifferent points in the charge curve, some embodiments dynamicallygenerate the values of the window. For example, some embodiments maymake a first measurement with the respective Σ-Δ ADC 704 during a firsttime, then configure DAC 1016 to generate a window centered at themeasured value, and then simultaneously measure during a second time thevoltage across the battery cell with the respective Σ-Δ ADC 704 and therespective comparator circuit 1008.

FIG. 11 shows a flow chart of embodiment method 1100 of detecting afailure of a battery management system, according to an embodiment ofthe present invention. Method 1100 may be implemented using batterymanagement system 1000. Alternatively, method 1100 may be implemented inother battery management system implementations. The discussion thatfollows assumes that battery management system 1000, as shown in FIG. 10, implements method 1100.

During step 1102, a first voltage Volt, across a battery cell, such asbattery cell cell₁ of battery pack 701, is measured by a first voltagemeasurement circuit, such as, for example, Σ-Δ ADC 704 ₀ via a firstpath during a first time.

During step 1104, a high voltage threshold V_(th_high) and a low voltagethreshold V_(th_low) are set based on the first voltage. For example, ifthe first voltage measured is 3.6 V, the high voltage thresholdV_(th_high) may be set to 3.65 V and the low voltage thresholdV_(th_low) may be set to 3.55 V. In some embodiments, the measuredvoltage may be centered between the high voltage threshold V_(th_high)and a low voltage threshold V_(th_low) selected. In other embodiments,the measured voltage may not be centered between the high voltagethreshold V_(th_high) and a low voltage threshold V_(th_low) selected.The voltage thresholds are applied to a window comparator, such ascomparator circuit 1008 ₀ by using, for example a DAC, such as DAC 1016.

During steps 1106, a second voltage Volt₂ is measured using the firstvoltage measurement circuit during a second time. During the same secondtime, a third voltage Volt₃ is sampled with the comparator circuit todetermine whether the voltage Volt3 is inside the window specified bythe high voltage threshold V_(th_high) and the low voltage thresholdV_(th_low).

If the second voltage Volt₂ is outside the window, step 1102 is executedagain, as shown by step 1110. Voltage Volt₂ may be outside the window,for example, because of a sudden spike in current. If voltage Volt₂ isinside the window and the comparator circuit indicates that the thirdvoltage Volt₃ is inside the window, then the battery management systemis operating normally, and no errors are affecting the measurements.Else, if voltage Volt₂ is inside the window and the comparator circuitindicates that the third voltage Volt₃ is outside the window, a fault isdetected, as shown by steps 1112 and 1116.

In some embodiments, method 1100 is executed sequentially in eachbattery cells. In other embodiments, multiple memory cells (such as 2,3, 4, or more, including all memory cells of battery pack 701) executemethod 1100 simultaneously.

Example embodiments of the present invention are summarized here. Otherembodiments can also be understood from the entirety of thespecification and the claims filed herein.

Example 1. A method for providing battery diagnostics, the methodincluding: measuring a first voltage across a first battery cell of arechargeable battery via a first measurement path of a network using afirst measurement circuit, measuring the first voltage including takingat least one first voltage sample during a first time period using thefirst measurement circuit; measuring a second voltage across the firstbattery cell via a second measurement path of the network using a secondmeasurement circuit, measuring the second voltage including taking atleast one second voltage sample during the first time period using thesecond measurement circuit, where the second measurement path of thenetwork is different from the first measurement path of the network;comparing the measured first voltage with the measured second voltage;and generating a diagnostic output signal based on the comparison.

Example 2. The method of example 1, where the at least one first voltagesample is taken using a first measurement scheme and the at least onesecond voltage sample is taken using a second measurement scheme, wherethe second measurement scheme is different from the first measurementscheme.

Example 3. The method of one of examples 1 or 2, where measuring thefirst voltage further includes taking a first plurality of voltagesamples during the first time period using the first measurementcircuit; and where measuring the second voltage further includes takinga second plurality of voltage samples during the first time period usingthe second measurement circuit.

Example 4. The method of one of examples 1 to 3, where measuring thesecond voltage further includes averaging an output of the secondmeasurement circuit using an averaging circuit coupled to the secondmeasurement circuit.

Example 5. The method of one of examples 1 to 4, where the diagnosticoutput signal is asserted when a difference between the measured firstvoltage and the measured second voltage is higher than a first voltagethreshold.

Example 6. The method of one of examples 1 to 5, where the firstmeasurement circuit has a first dominant pole and the second measurementcircuit has a second dominant pole, where the method further includesmatching the first dominant pole and the second dominant pole.

Example 7. The method of one of examples 1 to 6, where a first totaleffective filtering characteristic of the first measurement pathtogether with the first measurement circuit is substantially similar toa second total effective filtering characteristic of the secondmeasurement path together with the second measurement circuit.

Example 8. The method of one of examples 1 to 7, further including:providing a first reference voltage to the first measurement circuitwith a first reference voltage generator; and providing a secondreference voltage to the second measurement circuit with a secondreference voltage generator different from the first reference voltagegenerator.

Example 9. The method of one of examples 1 to 8, further including:providing the first reference voltage to a third measurement circuitwith the first reference voltage generator, where the third measurementcircuit and the first measurement circuit are based on a samemeasurement scheme; measuring a third voltage across a second batterycell of the rechargeable battery via a third measurement path of thenetwork using the third measurement circuit, measuring the third voltageincluding taking a third plurality of third voltage samples during asecond time period using the third measurement circuit, the second timeperiod occurring after the first time period, the second battery cellcoupled in series with the first battery cell; measuring a fourthvoltage across the second battery cell via a fourth measurement path ofthe network using the second measurement circuit, measuring the fourthvoltage including taking a fourth plurality of fourth voltage samplesduring the second time period using the second measurement circuit, thefourth measurement path being different than the third measurement path;comparing the measured third voltage with the measured fourth voltage;and asserting the diagnostic output signal when a difference between thethird voltage and the fourth voltage is higher than a first voltagethreshold.

Example 10. A circuit including: a first measurement circuit configuredto be coupled to a first battery cell via a first path of a network; asecond measurement circuit configured to be coupled to the first batterycell via a second path of the network, the second path being differentthan the first path; and a controller configured to: cause the firstmeasurement circuit to measure a first plurality of voltage samplesacross first and second terminals of the first battery cell during afirst time period, cause the second measurement circuit to measure asecond plurality of voltage samples across the first and secondterminals of the first battery cell during the first time period,compare an output of the first measurement circuit with an output of thesecond measurement circuit, and generate a diagnostic output signalbased on the comparison.

Example 11. The circuit of example 10, where the first measurementcircuit has a different architecture than the second measurementcircuit.

Example 12. The circuit of one of examples 10 or 11, where the firstmeasurement circuit has a first dominant pole, the second measurementcircuit has a second dominant pole, and the first dominant pole issubstantially equal to the second dominant pole.

Example 13. The circuit of one of examples 10 to 12, further including:a first reference voltage generator coupled to the first measurementcircuit; and a second reference voltage generator coupled to the secondmeasurement circuit.

Example 14. The circuit of one of examples 10 to 13, where the firstmeasurement circuit includes a sigma-delta analog-to-digital converter(ADC) and the second measurement circuit includes a successiveapproximation register (SAR) analog-to-digital converter (ADC).

Example 15. The circuit of one of examples 10 to 13, where the secondmeasurement circuit includes a window comparator, and where thecontroller is configured to set an upper limit of the window comparatorand a lower limit of the window comparator based on the output of thefirst measurement circuit.

Example 16. The circuit of one of examples 10 to 15, further including:a first sensing terminal coupled to the first measurement circuit andconfigured to be coupled to the first terminal of the first battery cellvia the network; a second sensing terminal coupled to the firstmeasurement circuit and to the second measurement circuit and configuredto be coupled to the second terminal of the first battery cell; and afirst power terminal coupled to the second measurement circuit andconfigured to be coupled to the first terminal of the first batterycell.

Example 17. The circuit of one of examples 10 to 15, further including:a first sensing terminal coupled to the first measurement circuit andconfigured to be coupled to the first terminal of the first battery cellvia the network; a second sensing terminal coupled to the firstmeasurement circuit and configured to be coupled to the second terminalof the first battery cell; a first power terminal coupled to the secondmeasurement circuit and configured to be coupled to the first terminalof the first battery cell; and a second power terminal coupled to thesecond measurement circuit and configured to be coupled to the secondterminal of the first battery cell.

Example 18. The circuit of one of examples 10 to 17, where a first totaleffective filter characteristic of the first path is as about equal to asecond total effective filter characteristic of the second path.

Example 19. The circuit of one of examples 10 to 18, where the networkincludes a balancing network.

Example 20. The circuit of one of examples 10 to 19, where the firstmeasurement circuit has a first step response, the second measurementcircuit has a second step response, and the first response issubstantially equal to the second step response.

Example 21. A battery management system including: a rechargeablebattery including N battery cells coupled in series, where N is apositive integer greater than zero; a balancing network coupled to therechargeable battery; and a battery monitoring circuit coupled to thebalancing network, the battery monitoring circuit including: asigma-delta analog-to-digital converter (ADC) having an input configuredto be coupled to a first battery cell of the N battery cells via a firstpath of the balancing network, the sigma-delta ADC coupled to a firstreference voltage generator; a measurement circuit having an inputconfigured to be coupled to the first battery cell via a second path ofthe balancing network, the second path being different from the firstpath, the measurement circuit coupled to a second reference voltagegenerator different from the first reference voltage generator, themeasurement circuit having a different architecture than the sigma-deltaADC; and a controller configured to: control the sigma-delta ADC tomeasure a first plurality of voltage samples across first and secondterminals of the first battery cell during a first time period, controlthe measurement circuit to measure a second plurality of voltage samplesacross the first and second terminals of the first battery cell duringthe first time period, compare an output of the sigma-delta ADC with anoutput of the measurement circuit, and generate a diagnostic outputsignal based on the comparison.

Example 22. The battery management system of example 21, furtherincluding N sigma-delta ADCs and N measurement circuits, where the Nsigma-delta ADCs include the sigma-delta ADC, and where each of the Nsigma-delta ADCs is coupled to a respective battery cell of the Nbattery cells, and where the N measurement circuits include themeasurement circuit, and where each of the N measurement circuits iscoupled to a respective battery cell of the N battery cells.

Example 23. The battery management system of example 21, where thesigma-delta ADC has a first dominant pole of Nth order, where N is apositive integer greater or equal to 1, the measurement circuit has asecond dominant pole of the Nth order, and the first dominant pole issubstantially equal to the second dominant pole.

While this invention has been described with reference to illustrativeembodiments, this description is not intended to be construed in alimiting sense. Various modifications and combinations of theillustrative embodiments, as well as other embodiments of the invention,will be apparent to persons skilled in the art upon reference to thedescription. It is therefore intended that the appended claims encompassany such modifications or embodiments.

What is claimed is:
 1. A battery monitoring circuit comprising: a firstmultiplexer having inputs coupled configured to be coupled to aplurality of battery cells, and a second multiplexer having inputsconfigured to be coupled to the plurality of battery cells; a firstmeasurement circuit coupled to an output of the first multiplexer, and asecond measurement circuit different from the first measurement circuitcoupled to an output of the second multiplexer; and a controllerconfigured to: cause the first multiplexer to couple a first batterycell to the first measurement circuit via a first signal path during afirst time period, and cause the second multiplexer to couple the firstbattery cell to the second measurement circuit via a second signal pathdifferent from the first signal path during the first time period, andcause the first measurement circuit to measure a first plurality ofvoltage samples across the first battery cell, and cause the secondmeasurement circuit to measure a second plurality of voltage samplesacross the first battery cell during the first time period.
 2. Thebattery monitoring circuit of claim 1, wherein the controller is furtherconfigured to: compare an output of the first measurement circuit withan output of the second measurement circuit; and generate a diagnosticoutput based on the comparison.
 3. The battery monitoring circuit ofclaim 1, wherein the first measurement circuit has a differentarchitecture from the second measurement circuit.
 4. The batterymonitoring circuit of claim 1, wherein the first measurement circuit hasa first dominant pole, the second measurement circuit has a seconddominant pole, and the first dominant pole is substantially equal to thesecond dominant pole.
 5. The battery monitoring circuit of claim 1,further comprising: a first reference voltage generator coupled to thefirst measurement circuit; and a second reference voltage generatorcoupled to the second measurement circuit.
 6. The battery monitoringcircuit of claim 1, wherein the first measurement circuit comprises asigma-delta analog-to-digital converter and the second measurementcircuit comprises a successive approximation register analog-to-digitalconverter.
 7. The battery monitoring circuit of claim 1, wherein thesecond measurement circuit comprises a window comparator, and whereinthe controller is configured to set an upper limit of the windowcomparator and a lower limit of the window comparator based on theoutput of the first measurement circuit.
 8. The battery monitoringcircuit of claim 1, further comprising terminals configured to becoupled to the plurality of battery cells, and coupled to the firstmultiplexer or the second multiplexer, wherein the first signal pathincludes a first terminal coupled to a first node of the first batterycell, and the second signal path includes a second terminal differentfrom the first terminal coupled to the first node of the first batterycell.
 9. The battery monitoring circuit of claim 1, wherein: the firstmultiplexer is configured to couple first and second terminals of thefirst battery cell to first and second terminals of the firstmeasurement circuit via a first combination of connection pins; and thesecond multiplexer is configured to couple the first and secondterminals of the first battery cell to first and second terminals of thefirst measurement circuit via a second combination of connection pins.10. A battery monitoring circuit comprising: a plurality of firstmeasurement circuits configured to be coupled to corresponding batterycells of a plurality of battery cells; a multiplexer having inputscoupled configured to be coupled to the plurality of battery cells; asecond measurement circuit different from the plurality of firstmeasurement circuits coupled to an output of the multiplexer; and acontroller configured to: cause a first measurement circuit of theplurality of first measurement circuits to measure a first plurality ofvoltage samples across a first battery cell of the plurality of batterycells during a first time period, wherein the first measurement circuitis coupled to the first battery cells via a first signal path, cause themultiplexer to couple the first battery cell to the second measurementcircuit via a second signal path different from the first signal pathduring the first time period, and cause the second measurement circuitto measure a second plurality of voltage samples across the firstbattery cell during the first time period.
 11. The battery monitoringcircuit of claim 10, wherein the controller is further configured to:compare an output of the first measurement circuit with an output of thesecond measurement circuit; and generate a diagnostic output based onthe comparison.
 12. The battery monitoring circuit of claim 10, whereinthe first measurement circuit has a different architecture from thesecond measurement circuit.
 13. The battery monitoring circuit of claim10, wherein the first measurement circuit has a first dominant pole, thesecond measurement circuit has a second dominant pole, and the firstdominant pole is substantially equal to the second dominant pole. 14.The battery monitoring circuit of claim 10, further comprising: a firstreference voltage generator coupled to the first measurement circuit;and a second reference voltage generator coupled to the secondmeasurement circuit.
 15. The battery monitoring circuit of claim 10,wherein the first measurement circuit comprises a sigma-deltaanalog-to-digital converter and the second measurement circuit comprisesa successive approximation register analog-to-digital converter.
 16. Thebattery monitoring circuit of claim 10, wherein the first measurementcircuit comprises a window comparator, and wherein the controller isconfigured to set an upper limit of the window comparator and a lowerlimit of the window comparator based on the output of the secondmeasurement circuit.
 17. The battery monitoring circuit of claim 10,further comprising terminals configured to be coupled to the pluralityof battery cells, and coupled to the multiplexer or the plurality offirst measurement circuits, wherein the first signal path includes afirst terminal coupled to a first node of the first battery cell, andthe second signal path includes a second terminal different from thefirst terminal coupled to the first node of the first battery cell. 18.A battery management system comprising: a rechargeable batterycomprising N battery cells coupled in series, wherein N is a positiveinteger greater than zero; a balancing network coupled to therechargeable battery; and a battery monitoring circuit coupled to thebalancing network, the battery monitoring circuit comprising: a firstmeasurement circuit having an input configured to be coupled to a firstbattery cell of the N battery cells via a first path of the balancingnetwork, the first measurement circuit coupled to a first referencevoltage generator; a second measurement circuit different from the firstmeasurement circuit having an input configured to be coupled to thefirst battery cell via a second path of the balancing network, thesecond path being different from the first path, the second measurementcircuit coupled to a second reference voltage generator different fromthe first reference voltage generator, the second measurement circuithaving a different architecture than the first measurement circuit; anda controller configured to: control the first measurement circuit tomeasure a first plurality of voltage samples across first and secondterminals of the first battery cell during a first time period, controlthe second measurement circuit to measure a second plurality of voltagesamples across the first and second terminals of the first battery cellduring the first time period, compare an output of the first measurementcircuit with an output of the second measurement circuit, and generate adiagnostic output signal based on the comparison.
 19. The batterymanagement system of claim 18, further comprising N first measurementcircuits and N second measurement circuits, wherein the N firstmeasurement circuits include the first measurement circuit, and whereineach of the N first measurement circuits is coupled to a respectivebattery cell of the N battery cells, and wherein the N secondmeasurement circuits include the second measurement circuit, and whereineach of the N second measurement circuits is coupled to the respectivebattery cell of the N battery cells.
 20. The battery management systemof claim 18, wherein the first measurement circuit has a first dominantpole of Nth order, wherein N is a positive integer greater or equal to1, the second measurement circuit has a second dominant pole of the Nthorder, and the first dominant pole is substantially equal to the seconddominant pole.